The device of the present invention may be used, for example, in the marine environment as an antipounding slide or pounding compensator. In fact, at sea, the swell causes, among other effects, the pounding or heave of floating equipment. When such equipment supports a well drilling apparatus, it is necessary to compensate for the pounding so that the drilling tool is permanently in contact with the bottom of the hole.
For compensation, three types of devices have generally been utilized, namely:
those which are placed in the drilling string, PA1 those which are inserted between the drilling string and the lifting system of the drilling apparatus, and those which are integrated in the lifting system. PA1 Q=force coming from all that contributes to the tension of the cable, PA1 N=number of strands of the second block PA1 U=fraction of F.sub.m independent of the tension of the cables, PA1 .beta.=angle formed by the strand of the cable between the fixed pulley and the intermediate pulley and the straight line joining the centers of these two pulleys, .phi.=angle defined by the direction of the straight line joining the center of the first and second fixed pulleys and the direction of the straight line joining the axes of the first fixed pulley and of the first intermediate pulley, .gamma.=angle formed by the cable strand joining the intermediate pulley and the pulley of the block and a straight line joining the centers of these two pulleys, .THETA.=angle formed by the direction of the straight line joining the center of the first and second fixed pulleys and the direction of the straight line joining the centers of the first block and of the first intermediate pulley; PA1 P.sub.g =preinflation pressure of the accumulators, PA1 S.sub.v =a cross-section of the actuating cylinders, PA1 K=V.sub.a /S.sub.v C.sub.cdc, with: PA1 V.sub.a =a volume of the accumulators, PA1 C.sub.cdc =a total stroke of the first block, PA1 Reduced stroke=actual stroke/C.sub.cdc PA1 .gamma..sup.1 =an expansion coefficient of gases.
The present invention, when it is applied to marine environment, relates to a compensator device integrated in the lifting system. This device forms part of those devices which solve the problem by making the fixed block movable, corresponding to the "crown block". This block will be designated hereinafter by the expression "first block" and the mobile block corresponding to the "travelling block" will be designated by the expression "second block".
The systems connected directly to the lifting device, in the prior art, generally comprise at least one actuating cylinder or jack itself connected to pneumatic accumulators, however, a disadvantage of the proposed systems resides in the fact that the pneumatic accumulators occupy a large volume.
Systems of the aforementioned type are described in, for example, U. S. Pat. Nos. 3,791,628 and 3,749,367, German Patent DE-A-2,221,700, and French Patent FR-A-95 453 as well as by the article entitled "Heave Compensating Devices" on page 4 and 8 of "Oil Report Review", No. 8, Sep. 10, 1973.
The volume of these accumulators is an important parameter in the determination of a lifting system.
Another important consideration is the variation of the force to be exerted on the second block as a function of the stroke of the mobile installation with respect to a constant value which the second block should withstand.
The difference between the real force and this constant value will be termed error.
The present invention reduces the volume of the accumulators and/or reduces the error.